1. Field of the Invention
The invention relates to the art of temperature warning systems for vehicles, and in particular to temperature warning systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers, and straight trucks, which can function during vehicle operation. More particularly, the invention relates to high-temperature warning systems that are mountable in an axle spindle end of such heavy-duty vehicles for indicating an undesirable high temperature in the axle spindle end and/or associated wheel components during vehicle operation.
2. Background Art
Reference herein is made to tractor-trailers by way of example, with the understanding that such reference applies to other heavy-duty vehicles, such as straight trucks. All tractor-trailers include at least one trailer, and sometimes two or three trailers, all of which are pulled by a single tractor. Each trailer includes a frame, from which at least one axle is suspended. A wheel end assembly is rotatably mounted on each end of the axle. More specifically, each wheel end assembly includes bearing assemblies that are mounted on a respective axle spindle end, and a wheel hub which in turn is mounted on the bearing assemblies. In this manner, the bearing assemblies enable the wheel hub to rotate about the axle spindle end.
To facilitate smooth rotation of each wheel hub about its respective axle spindle end, the bearing assemblies typically include a lubricant. A bearing seal formed of a relatively flexible material, such as rubber, is disposed on the inboard end of the wheel hub to isolate the bearing assemblies for preventing contaminants from passing into the bearings, and to contain the lubricant within the bearings. Repeated excessive speed or excessive braking of the vehicle often generates a large amount of heat in components of the wheel end assembly and/or the axle spindle end, in turn heating the bearing lubricant and/or the bearing seal, which may cause degradation of the lubricant or the bearing seal. If the lubricant degrades, rotation of the wheel hub about the axle spindle end may become impaired and can result in damage to or failure of the wheel end assembly and/or the axle spindle end.
Alternatively, if the seal degrades, the lubricant may escape, or external contaminants may pass into the bearing assemblies, which can also impair the rotation of the wheel hub about the axle spindle end and may potentially damage the wheel end assembly or the axle spindle end. Similar potential damage may be caused by installation problems which detrimentally affect the lubricant and/or bearing assemblies, and thus allow excessive heat to be generated in the wheel end components or the axle spindle end. Such installation problems include situations in which the lubricant accidentally may have been omitted from the bearing assemblies, and/or over-tightening of the bearing retaining nuts, which can overload the bearing assemblies.
In addition, in some applications, sealed bearing assemblies are used. Sealed bearing assemblies are self-contained units that are packed with lubricant and include a seal that is built into the bearing assembly. Such sealed bearing assemblies are known in the art as being non-serviceable, and thus typically cannot readily be opened up in order to replace or add lubricant if the lubricant escapes the assembly or degrades. Rather, sealed bearing assemblies are typically removed from service and replaced if such a problem occurs. Since it is desirable to remove a sealed bearing from service in the event that such a problem does occur, it is advantageous to attempt to monitor conditions that may indicate a potential problem, such as the generation of excessive heat, as described above.
Because multiple trailers, each possibly having multiple axles and multiple wheel ends, may be pulled by a single tractor, the chance that a given wheel end assembly and/or axle spindle end may become impaired from the above-described conditions without detection by the vehicle operator increases. Since the potential damage resulting from an undetected high temperature is undesirable, it is advantageous to attempt to monitor the components of the axle, including the spindle ends, and/or the wheel end assemblies for high-temperature conditions. Such conditions may indicate degradation of or a lack of the proper amount of lubricant in the bearing assemblies, degradation of the bearing seals, contamination in the bearing assemblies, an overloading of the bearings, or the breaking down of the bearing itself. It is also advantageous to alert the operator of the vehicle when a high-temperature condition is detected, which enables the operator to remove the vehicle from service to reduce the potential damage that may result from such high-temperature conditions.
In the prior art, attempts to monitor conditions at the wheel end assembly and/or in the axle spindle end have been made. However, early attempts resulted in systems that are inconvenient to check or that can only be checked when the vehicle is not moving, such as the use of a mechanical indicator on the wheel hub. In an attempt to improve such systems, more sophisticated approaches have been developed. These more sophisticated systems use circuits that employ resistance elements such as a resistor or a thermistor, which create an open electrical circuit at normal operating temperature. When the temperature increases, the resistance element closes the electrical circuit, which generates an alarm. Such open-circuit systems, however, cannot be easily diagnosed for broken wires or other potential problems at normal operating temperatures, since electrical current cannot pass through the open circuit. In addition, a resistance element typically closes a circuit gradually, which may create a delay in the alarm, or may create uncertainty as to the exact temperature at which the alarm is triggered.
Other prior art approaches to such temperature measurement are relatively elaborate, and typically utilize a programmable microprocessor to control the system. The microprocessor interprets incoming data from a sensor and executes a pre-programmed decision-making process to determine when an alarm should be activated. These microprocessors, however, undesirably add to the complexity and expense of a temperature warning system. Moreover, some of these prior art systems also utilize transmitters and batteries, which have limited life spans, necessitating frequent diagnosis and repair.
As a result, the temperature warning systems of the prior art include significant disadvantages, including inconvenience, lack of self-diagnosis, lack of rapid and accurate alarm generation, and high cost due to system complexities. Therefore, a longstanding need has existed in the art for a temperature warning system that is easy to use and convenient, which activates quickly and accurately, which is capable of self-diagnosis, and is economical to purchase and maintain. The present invention provides such a temperature warning system.